If your Zune player won't charge - i.e. is just displaying the large "low battery" icon on its screen - here are troubleshooting tips.
Try each of the following. After each, disconnect your player from the PC and see if it will boot up, or at least get past your Battery icon.
1. How long has it been charging? Give your player at least a half hour to take a charge enough to boot up and get you going.
2. If it's been charging longer than that, try re-setting your player. Press and hold the Back button while pressing and holding "Up" on the control pad. Your player will re-set.
3. Try connecting your player to a different USB port - preferably on the back of your PC. (Those USB ports are typically better powered than front USB ports.)
4. If you're using a USB hub, disconnect it and plug your sync cable directly into a USB port.
5. Try using another charging source if you have one; eg a Zune AC adapter charger.
6. If you have another sync cable handy, try it - just in case there's a problem with your cable.
7. If you have other devices plugged into your USB ports - unplug as many of them as you can. (i.e. printers, scanners, etc.)
8. Try draining your battery completely. To do so, disconnect your player from the PC. Press Play - ie to see the "low battery" icon. After the icon disappears, press Play again. Continue until the battery is drained. Then reconnect to a power source.
9. This is a long shot, but try a complete reformat of your player. To do that:
Re-set it (press/hold BACK while pressing/holding "UP"), and while it's re-setting, press the BACK, CENTER BUTTON, and PLAY button all at the same time.
You should see a warning message that your player is about to reformat itself. (You'll lose all content on the player - which sounds like it is probably empty anyway.)
10. Call Zune tech support at 877-GET-ZUNE, for additional troubleshooting and diagnostics.
11. If you've tried all that, to no avail, you probably have a unit with a bum battery. Your options are:
a. Replace the battery. (Zune batteries are supposedly not replaceable. You can however buy replacement batteries from rapidrepair.com, along with instructions.)
b. Return the player to where you purchased it, to exchange it for a new one.
c. You could also try calling Zune tech support to see if they have additional ideas. In some cases they will have you send in your player and they'll send you a replacement.